Method and apparatus for selecting a serving sector in a data communication system

ABSTRACT

Methods and apparatus for selecting a serving sector in a high rate data (HDR) communication system are disclosed. An exemplary HDR communication system defines a set of data rates, at which a sector of an Access Point may send data packets to an Access Terminal. The sector is selected by the Access Terminal to achieve the highest data throughput while maintaining a targeted packet error rate. The Access Terminal employs various methods to evaluate quality metrics of forward and reverse links from and to different sectors, and uses the quality metrics to select the sector to send data packets to the Access Terminal.

CLAIM PRIORITY UNDER 35 U.S.C. §120

[0001] The present Application for Patent is a Continuation and claimspriority to patent application Ser. No. 09/892,378 entitled “METHOD ANDAPPARATUS FOR SELECTING A SERVING SECTOR IN A DATA COMMUNICATIONSYSTEM,” filed Jun. 26, 2001, now allowed, and assigned to the assigneehereof and hereby, expressly incorporated by reference herein.

BACKGROUND

[0002] 1. Field

[0003] The present invention relates generally to communication systems,and more specifically, to a method and an apparatus for selecting aserving sector in a data communication system.

[0004] 2. Background

[0005] Communication systems have been developed to allow transmissionof information signals from an origination station to a physicallydistinct destination station. In transmitting information signals fromthe origination station over a communication channel, the informationsignal is first converted into a form suitable for efficienttransmission over the communication channel. Conversion, or modulation,of the information signal involves varying a parameter of a carrier wavein accordance with the information signal in such a way that thespectrum of the resulting modulated carrier is confined within thecommunication channel bandwidth. At the destination station the originalinformation signal is replicated from the modulated carrier wavereceived over the communication channel. Such a replication is generallyachieved by using an inverse of the modulation process employed by theorigination station.

[0006] Modulation also facilitates multiple-access, i.e., simultaneoustransmission and/or reception, of several signals over a commoncommunication channel. Multiple-access communication systems ofteninclude a plurality of remote subscriber units requiring intermittentservice of relatively short duration rather than continuous access tothe common communication channel. Several multiple-access techniques areknown in the art, such as time division multiple-access (TDMA),frequency division multiple-access (FDMA), and amplitude modulationmultiple-access (AM). Another type of a multiple-access technique is acode division multiple-access (CDMA) spread spectrum system thatconforms to the “TIA/EIA/IS-95 Mobile Station-Base Station CompatibilityStandard for Dual-Mode Wide-Band Spread Spectrum Cellular System,”hereinafter referred to as the IS-95 standard. The use of CDMAtechniques in a multiple-access communication system is disclosed inU.S. Pat. No. 4,901,307, entitled “SPREAD SPECTRUM MULTIPLE-ACCESSCOMMUNICATION SYSTEM USING SATELLITE OR TERRESTRIAL REPEATERS,” and U.S.Pat. No. 5,103,459, entitled “SYSTEM AND METHOD FOR GENERATING WAVEFORMSIN A CDMA CELLULAR TELEPHONE SYSTEM,” both assigned to the assignee ofthe present invention.

[0007] A multiple-access communication system may be a wireless orwire-line and may carry voice and/or data. An example of a communicationsystem carrying both voice and data is a system in accordance with theIS-95 standard, which specifies transmitting voice and data over thecommunication channel. A method for transmitting data in code channelframes of fixed size is described in detail in U.S. Pat. No. 5,504,773,entitled “METHOD AND APPARATUS FOR THE FORMATTING OF DATA FORTRANSMISSION”, assigned to the assignee of the present invention. Inaccordance with the IS-95 standard, the data or voice is partitionedinto code channel frames that are 20 milliseconds wide with data ratesas high as 14.4 Kbps. Additional examples of a communication systemscarrying both voice and data comprise communication systems conformingto the “3rd Generation Partnership Project” (3GPP), embodied in a set ofdocuments including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS25.213, and 3G TS 25.214 (the W-CDMA standard), or “TR-45.5 PhysicalLayer Standard for cdma2000 Spread Spectrum Systems” (the IS-2000standard).

[0008] In a multiple-access communication system, communications betweenusers are conducted through one or more base stations. A first user onone subscriber station communicates to a second user on a secondsubscriber station by transmitting data on a reverse link to a basestation. The base station receives the data and can route the data toanother base station. The data is transmitted on a forward link of thesame base station, or the other base station, to the second subscriberstation. The forward link refers to transmission from a base station toa subscriber station and the reverse link refers to transmission from asubscriber station to a base station. Likewise, the communication can beconducted between a first user on one mobile subscriber station and asecond user on a landline station. A base station receives the data fromthe user on a reverse link, and routes the data through a publicswitched telephone network (PSTN) to the second user. In manycommunication systems, e.g., IS-95, W-CDMA, IS-2000, the forward linkand the reverse link are allocated separate frequencies.

[0009] An example of a data only communication system is a high datarate (HDR) communication system that conforms to the TIAIEIA/IS-856industry standard, hereinafter referred to as the IS-856 standard. ThisHDR system is based on a communication system disclosed in co-pendingapplication Ser. No. 08/963,386, entitled “METHOD and apparatus FOR HIGHRATE PACKET DATA transmission,” filed Nov. 3, 1997, assigned to theassignee of the present invention. The HDR communication system definesa set of data rates, ranging from 38.4 kbps to 2.4 Mbps, at which anaccess point (AP) may send data to a subscriber station (accessterminal, AT). Because the AP is analogous to a base station, theterminology with respect to cells and sectors is the same as withrespect to voice systems.

[0010] A significant difference between voice services and data servicesis the fact that the former imposes stringent and fixed delayrequirements. Typically, the overall one-way delay of speech frames mustbe less than 100 ms. In contrast, the data delay can become a variableparameter used to optimize the efficiency of the data communicationsystem. Specifically, more efficient error correcting coding techniqueswhich require significantly larger delays than those that can betolerated by voice services can be utilized. An exemplary efficientcoding scheme for data is disclosed in U.S. patent application Ser. No.08/743,688, entitled “SOFT DECISION OUTPUT DECODER FOR DECODINGCONVOLUTIONALLY ENCODED CODEWORDS,” filed Nov. 6, 1996, now U.S. Pat.No. 5,933,462, issued Aug. 3, 1999, assigned to the assignee of thepresent invention.

[0011] Another significant difference between voice services and dataservices is that the former requires a fixed and common grade of service(GOS) for all users. Typically, for digital systems providing voiceservices, this translates into a fixed and equal transmission rate forall users and a maximum tolerable value for the error rates of thespeech frames. In contrast, for data services, the GOS can be differentfrom user to user and can be a parameter optimized to increase theoverall efficiency of the data communication system. The GOS of a datacommunication system is typically defined as the total delay incurred inthe transfer of a predetermined amount of data, hereinafter referred toas a data packet.

[0012] Yet another significant difference between voice services anddata services is that the former requires a reliable communication link.When a mobile station, communicating with a first base station, moves tothe edge of the associated cell or sector, the mobile station initiatesa simultaneous communication with a second base station. Thissimultaneous communication, when the mobile station receives a signalcarrying equivalent information from two base stations, termed softhandoff, is a process of establishing a communication link with thesecond base station while maintaining a communication link with thefirst base station. When the mobile station eventually leaves the cellor sector associated with the first base station and breaks thecommunication link with the first base station, it continues thecommunication on the communication link established with the second basestation. Because the soft handoff is a “make before break” mechanism,the soft handoff minimizes the probability of dropped calls. The methodand system for providing a communication with a mobile station throughmore than one base station during the soft handoff process are disclosedin U.S. Pat. No. 5,267,261, entitled “MOBILE STATION ASSISTED SOFTHANDOFF IN A CDMA CELLULAR COMMUNICATIONS SYSTEM,” assigned to theassignee of the present invention. Softer handoff is the process wherebythe communication occurs over multiple sectors that are serviced by thesame base station. The process of softer handoff is described in detailin co-pending U.S. patent application Ser. No. 08/763,498, entitled“METHOD AND APPARATUS FOR PERFORMING HANDOFF BETWEEN SECTORS OF A COMMONBASE STATION,” filed Dec. 11, 1996, now U.S. Pat. No. 5,933,787, issuedAug. 3, 1999, assigned to the assignee of the present invention. Thus,both soft and softer handoff for voice services result in redundanttransmissions from two or more base stations to improve reliability.

[0013] This additional reliability is not required for data transmissionbecause the data packets received in error can be retransmitted. Fordata services, the parameters, which measure the quality andeffectiveness of a data communication system, are the transmission delayrequired to transfer a data packet and the average throughput rate ofthe system. Transmission delay does not have the same impact in datacommunication as in voice communication, but the transmission delay isan important metric for measuring the quality of the data communicationsystem. The average throughput rate is a measure of the efficiency ofthe data transmission capability of the communication system.Consequently, the transmit power and resources used to support softhandoff can be more efficiently used for transmission of additionaldata. To maximize the throughput, the transmitting sector should bechosen in a way that maximizes the forward link throughput as perceivedby the Access Terminal (AT).

[0014] There is, therefore, a need in the art for a method and anapparatus for selecting a sector in a data communication system thatmaximizes the forward link throughput as perceived by the AT.

SUMMARY

[0015] In one aspect of the invention, the above-stated needs areaddressed by determining at the remote station a quality metric of aforward link for each sector in the remote station's list, determining aquality metric of a reverse link to each sector in the remote station'slist, and directing communication between the remote station and onesector from the sectors in the remote station's list in accordance withsaid determined quality metric of a forward link and said determinedquality metric of a reverse link. The quality metric of a forward linkfor each sector in the remote station's list may be determined bymeasuring a signal-to interference and signal-to-noise ratio of theforward link. The quality metric of a reverse link to each sector in theremote station's list may be determined by processing at the remotestation the forward link from each sector in the remote station's list.The signal processed may be obtained by measuring at each sector thequality metric of the reverse link, processing the quality metric toprovide an indicator of the quality metric, and providing the indicatoron a forward link. The communication between the remote station and onesector from the sectors in the remote station's list may be directed inaccordance with said determined quality metric of a forward link andsaid determined quality metric of a reverse link by assigning credits toeach sector in the remote station's list, except a sector currentlyserving the remote station in accordance with said determined qualitymetric of a forward link and said determined quality metric of thereverse link, and directing communication between the remote station andone sector from the sectors in the remote station's list in accordancewith said assigned credits.

[0016] In another aspect of the invention, the above-stated needs areaddressed by determining at the remote station a quality metric of aforward link for each sector in the remote station's list; and directingcommunication between the remote station and one sector from the sectorsin the remote station's list in accordance with said determined qualitymetric of a forward link. The quality metric of a forward link for eachsector in the remote station's list may be determined by measuring asignal-to-interference and signal-to-noise ratio of the forward link.The communication between the remote station and one sector from thesectors in the remote station's list may be directed in accordance withsaid determined quality metric of a forward link by assigning credits toeach sector in the remote station's list, except a sector currentlyserving the remote station in accordance with said determined qualitymetric of a forward link and directing communication between the remotestation and one sector from the sectors in the remote station's list inaccordance with said assigned credits.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 illustrates a conceptual diagram of an High Data Rate (HDR)communication system;

[0018]FIG. 2 illustrates an exemplary forward link waveform;

[0019]FIG. 3 illustrates an Access Point processing of a data request(DRC) for a Message Based DRC Lock method;

[0020]FIG. 4 illustrates an Initialization phase at an Access Terminalfor the Message Based DRC Lock method;

[0021]FIG. 5 illustrates a Credit Accumulation phase at the AccessTerminal for the Message Based Data Request Channel Lock method;

[0022]FIG. 6 illustrates a Decision phase at the Access Terminal for theMessage Based DRC Lock method;

[0023]FIGS. 7 and 8 illustrate the Decision phase for a sector selectionwhen the DRC of a current serving sector is “in-lock” for the MessageBased DRC Lock method.

[0024]FIG. 9 illustrates the Decision phase for the sector selectionwhen the DRC of the current serving sector is “out-of-lock” for theMessage Based DRC Lock method.

[0025]FIG. 10 illustrates the Credit Accumulation phase at the AccessTerminal for the Message Based DRC Lock method in accordance withanother embodiment;

[0026]FIG. 11 illustrates the Decision phase for sector selection whenthe DRC from the current serving sector is “in-lock” for the MessageBased DRC Lock method in accordance with another embodiment;

[0027]FIG. 12 illustrates the Credit Accumulation phase at the AccessTerminal for the Message Based DRC Lock method in accordance with yetanother embodiment;

[0028]FIG. 13 illustrates the Access Point processing of the DRC for aPunctured DRC Lock Bit method;

[0029]FIG. 14 illustrates a Demodulation phase for the Punctured DRCLock Bit method;

[0030]FIG. 15 illustrates an Accreditation phase for the Punctured DRCLock Bit method;

[0031]FIG. 16 illustrates a Certification phase for the Punctured DRCLock Bit method; and

[0032]FIG. 17 illustrates a Decision phase for the Punctured DRC LockBit method.

DETAILED DESCRIPTION

[0033] The word “exemplary” is used exclusively herein to mean “servingas an example, instance, or illustration.” Any embodiment describedherein as “exemplary” is not necessarily to be construed as preferred oradvantageous over other embodiments.

[0034] The term packet is used exclusively herein to mean a group ofbits, including data (payload) and control elements, arranged into aspecific format. The control elements comprise, e.g., a preamble, aquality metric, and others known to one skilled in the art. Qualitymetric comprises, e.g., a cyclical redundancy check (CRC), a parity bit,and others known to one skilled in the art.

[0035] The term access network is used exclusively herein to mean acollection of access points (AP) and one or more access pointcontrollers. The access network transports data packets between multipleaccess terminals (AT). The access network may be further connected toadditional networks outside the access network, such as a corporateintranet or the Internet, and may transport data packets between eachaccess terminal and such outside networks.

[0036] The term base station, referred to herein as an AP in the case ofan HDR communication system, is used exclusively herein to mean thehardware with which subscriber stations communicate. Cell refers to thehardware or a geographic coverage area, depending on the context inwhich the term is used. A sector is a partition of a cell. Because asector has the attributes of a cell, the teachings described in terms ofcells are readily extended to sectors.

[0037] The term subscriber station, referred to herein as an AT in thecase of an HDR communication system, is used exclusively herein to meanthe hardware with which an access network communicates. An AT may bemobile or stationary. An AT may be any data device that communicatesthrough a wireless channel or through a wired channel, for example usingfiber optic or coaxial cables. An AT may further be any of a number oftypes of devices including, but not limited to a PCT Card, a compactflash, an external or internal modem, or a wireless or wireline phone.An AT that is in the process of establishing an active traffic channelconnection with an AP is said to be in a connection setup state. An ATthat has established an active traffic channel connection with an AP iscalled an active AT and is said to be in a traffic state.

[0038] The term communication channel/link is used exclusively herein tomean a single route over which a signal is transmitted described interms of modulation characteristics and coding, or a single route withinthe protocol layers of either the AP or the AT.

[0039] The term reverse channel/link is used exclusively herein to meana communication channel/link through which the AT sends signals to theAP.

[0040] A forward channel/link is used exclusively herein to mean acommunication channel/link through which an AP sends signals to an AT.

[0041] The term softer handoff is used exclusively herein to mean acommunication between a subscriber station and two or more sectors,wherein each sector belongs to the same cell. In the context of theIS-95 standard, the reverse link communication is received by bothsectors, and the forward link communication is simultaneously carried onone of the two or more sectors' forward links. In the context of theIS-856 standard, data transmission on the forward link isnon-simultaneously carried out between one of the two or more sectorsand the AT.

[0042] The term softer hand-off is used exclusively herein to mean acommunication between a subscriber station and two or more sectors,wherein each sector belongs to the same cell. In the context of theIS-95 standard, the reverse link communication is received by bothsectors, and the forward link communication is simultaneously carried onone of the two or more sectors' forward links. In the context of theIS-856 standard, data transmission on the forward link isnon-simultaneously carried out between one of the two or more sectorsand the AT.

[0043] The term re-pointing is used exclusively herein to mean aselection of a sector that is a member of an AT's active list, whereinthe sector is different than a currently selected sector.

[0044] The term soft/softer handoff delay is used exclusively herein toindicate the minimum interruption in service that a subscriber stationwould experience following a handoff to another sector. Soft/softerhandoff delay is determined based on whether the sector, (currently notserving the subscriber station, or the non-serving sector) to which thesubscriber station is re-pointing is part of the same cell as thecurrent serving sector.

[0045] If the non-serving sector is in the same cell as the servingsector, then the softer handoff delay is used, and if the non-servingsector is in a cell different from the one that the serving sector ispart of, then the soft-handoff delay is used.

[0046] The term non-homogenous soft/softer handoff delay is usedexclusively herein to indicate that the soft/softer handoff delays aresector specific, and therefore may not uniform across the sectors of anAccess Network.

[0047] The term credit is used exclusively herein to mean adimensionless attribute indicating a quality metric of a reverse link, aquality metric of a forward link, or a composite quality metric of bothforward and reverse links.

[0048] The term erasure is used exclusively herein to mean failure torecognize a message.

[0049] The term outage is used exclusively herein to mean a timeinterval during which the likelihood that a subscriber station willreceive service is reduced.

[0050] The term fixed rate mode is used exclusively herein to mean thata particular sector transmits a Forward Traffic Channel to the AT at oneparticular rate.

Description

[0051]FIG. 1 illustrates a conceptual diagram of an HDR communicationsystem capable of performing re-pointing in accordance with embodimentsof the present invention, e.g., a communication system in accordancewith the IS-856 standard. An AP 100 transmits data to an AT 104 over aforward link 106(1) and receives data from the AT 104 over a reverselink 108(1). Similarly, an AP 102 transmits data to the AT 104 over aforward link 106(2) and receives data from the AT 104 over a reverselink 108(2). In accordance with one embodiment, data transmission on theforward link occurs from one AP to one AT at or near the maximum datarate that can be supported by the forward link and the communicationsystem. Other channels of the forward link, e.g., control channel, maybe transmitted from multiple APs to one AT. Reverse link datacommunication may occur from one AT to one or more APs. The AP 100 andthe AP 102 are connected to a controller 110 over backhauls 112(1) and112(2). The term backhaul is used to mean a communication link between acontroller and an AP. Although only two AT's and one AP are shown inFIG. 1, one of ordinary skill in the art recognizes that this is forpedagogical purposes only, and the communication system can comprise aplurality of AT's and AP's.

[0052] Initially, the AT 104 and one of the AP's, e.g., the AP 100,establish a communication link using a predetermined access procedure.In this connected state, the AT 104 is able to receive data and controlmessages from the AP 100 and is able to transmit data and controlmessages to the AP 100. The AT 104 continually searches for other APsthat could be added to the AT 104 active set. The active set comprises alist of the APs capable of communication with the AT 104. When such anAP is found, the AT 104 calculates a quality metric of the AP's forwardlink, which in one embodiment comprises a signal-to-interferenceand-noise ratio (SINR). In one embodiment, the AT 104 searches for otherAPs and determines the AP's SINR in accordance with a pilot signal.Simultaneously, the AT 104 calculates the forward link quality metricfor each AP in the AT 104 active set. If the forward link quality metricfrom a particular AP is above a predetermined add threshold or below apredetermined drop threshold for a predetermined period of time, the AT104 reports this information to the AP 100. Subsequent messages from theAP 100 direct the AT 104 to add to or to delete from the AT 104 activeset the particular AP.

[0053] The AT 104 selects a serving AP from the active set based on aset of parameters. The term serving AP refers to an AP that a particularAT selected for data communication or an AP that is communicating datato the particular AT. The set of parameters can comprise present andprevious SINR measurements, a bit-error-rate and/or a packet-error-rate,and other parameters known to one skilled in the art. In one embodiment,the serving AP is selected in accordance with the largest SINRmeasurement. The AT 104 then transmits to the selected AP a data requestmessage (DRC message) on the data request channel (DRC channel). The DRCmessage can contain the requested data rate or, alternatively, anindication of the quality of the forward link, e.g., the measured SINR,the bit-error-rate, or the packet-error-rate. In one embodiment, the AT104 can direct the transmission of the DRC message to a specific AP bythe use of a Walsh code, which uniquely identifies the specific AP. TheDRC message symbols are exclusively OR'ed (XOR) with the unique Walshcode. The XOR operation is referred to as Walsh-covering of a signal.Since each AP in the active set of the AT 104 is identified by a uniqueWalsh code, only the selected AP which performs the identical XORoperation as that performed by the AT 104 with the correct Walsh codecan correctly decode the DRC message.

[0054] The data to be transmitted to the AT 104 arrive at the controller110. In accordance with one embodiment, the controller 110 sends thedata to all APs in AT 104 active set over the backhaul 112. In anotherembodiment, the controller 110 first determines which AP was selected bythe AT 104 as the serving AP, and then sends the data to the serving AP.The data are stored in a queue at the AP(s). A paging message is thensent by one or more APs to the AT 104 on respective control channels.The AT 104 demodulates and decodes the signals on one or more controlchannels to obtain the paging messages.

[0055] At each time time-slot, the AP can schedule data transmission toany of the ATs that received the paging message. An exemplary method forscheduling transmission is described in U.S. Pat. No. 6,229,795,entitled “System for allocating resources in a communication system,”assigned to the assignee of the present invention. The AP uses the ratecontrol information received from each AT in the DRC message toefficiently transmit forward link data at the highest possible rate. Inone embodiment, the AP determines the data rate at which to transmit thedata to the AT 104 based on the most recent value of the DRC messagereceived from the AT 104. Additionally, the AP uniquely identifies atransmission to the AT 104 by using a spreading code which is unique tothat mobile station. In the exemplary embodiment, this spreading code isthe long pseudo noise (PN) code, which is defined by the IS-856standard.

[0056] The AT 104, for which the data packet is intended, receives thedata transmission and decodes the data packet. In one embodiment, eachdata packet is associated with an identifier, e.g. a sequence number,which is used by the AT 104 to detect either missed or duplicatetransmissions. In such an event, the AT 104 communicates via the reverselink data channel the sequence numbers of the missing data units. Thecontroller 110, which receives the data messages from the AT 104 via theAP communicating with the AT 104, then indicates to the AP what dataunits were not received by the AT 104. The AP then schedules aretransmission of such data units.

[0057] When the communication link between the AT 104 and the AP 100,operating in the variable rate mode, deteriorates below requiredreliability level, the AT 104 first attempts to determine whethercommunication with another AP in the variable rate mode supporting anacceptable rate data is possible. If the. AT 104 ascertains such an AP(e.g., the AP 102), a re-pointing to the AP 102, therefore, to adifferent communication link occurs, and the data transmissions continuefrom the AP 102 in the variable rate mode. The above-mentioneddeterioration of the communication link can be caused by, e.g., the AT104 moving from a coverage area of the AP 100 to the coverage area ofthe AP 102, shadowing, fading, and other reasons known to one skilled inthe art. Alternatively, when a communication link between the AT 104 andanother AP (e.g., the AP 102) that may achieve higher throughput ratethat the currently used communication link becomes available, are-pointing to the AP 102, therefore, to a different communication linkoccurs, and the data transmissions continue from the AP 102 in thevariable rate mode. If the AT 104 fails to detect an AP that can operatein the variable rate mode and support an acceptable data rate, the AT104 transitions into a fixed rate mode.

[0058] In one embodiment, the AT 104 evaluates the communications linkswith all candidate APs for both variable rate data and fixed rate datamodes, and selects the AP, which yields the highest throughput.

[0059] The AT 104 will switch from the fixed rate mode back to thevariable rate mode if the sector is no longer a member of the AT 104active set.

[0060] In the exemplary embodiment, the above described the fixed ratemode and associated methods for transition to and from the fixed modeare similar to those disclosed in detail in U.S. Pat. No. 6,205,129,entitled “METHOD AND APPARATUS FOR VARIABLE AND FIXED FORWARD LINK RATECONTROL IN A MOBILE RADIO COMMUNICATION SYSTEM,” assigned to theassignee of the present invention. Other fixed rate modes and associatedmethods for transition to and from the fixed mode can also becontemplated and are within the scope of the present invention.

[0061] One skilled in the art recognizes that an AP can comprise one ormore sectors. In the description above, the term AP was used genericallyto allow clear explanation of basic concepts of the HDR communicationsystem. However, one skilled in the art can extend the explainedconcepts to AP comprising any number of sectors. Consequently, theconcept of sector will be used throughout the rest of the document.

Forward Link Structure

[0062]FIG. 2 illustrates an exemplary forward link waveform 200. Forpedagogical reasons, the forward link waveform 200 is modeled after aforward link waveform of the above-mentioned HDR system. However, one ofordinary skill in the art will understand that the teaching isapplicable to different waveforms. Thus, for example, in one embodimentthe waveform does not need to contain pilot signal bursts, and the pilotsignal can be transmitted on a separate channel, which can be continuousor bursty. The forward link waveform 200 is defined in terms of frames.A frame is a structure comprising 16 time-slots 202, each time-slot 202being 2048 chips long, corresponding to a 1.66-ms. time-slot duration,and, consequently, a 26.66-ms. frame duration. Each time-slot 202 isdivided into two half-time-slots 202 a and 202 b, with pilot bursts 204a and 204 b transmitted within each half-time-slot 202 a and 202 b. Inthe exemplary embodiment, each pilot burst 204 a and 204 b is 96 chipslong, and is centered at the mid-point of its associated half-time-slot202 a and 202 b. The pilot bursts 204 a and 204 b comprise a pilotchannel signal covered by a Walsh cover with index 0. A forward mediumaccess control channel (MAC) 206 forms two bursts, which are transmittedimmediately before and immediately after the pilot burst 204 of eachhalf-time-slot 202. In the exemplary embodiment, the MAC is composed ofup to 64 code channels, which are orthogonally covered by 64-ary Walshcodes. Each code channel is identified by a MAC index, which has a valuebetween 1 and 64, and identifies a unique 64-ary Walsh cover. A reversepower control channel (RPC) is used to regulate the power of the reverselink signals for each subscriber station. The RPC is assigned to one ofthe available MACs with MAC index between 5 and 63. The MAC with MACindex 4 is used for a reverse activity channel (RA), which performs flowcontrol on the reverse traffic channel. The forward link traffic channeland control channel payload is sent in the remaining portions 208 a ofthe first half-time-slot 202 a and the remaining portions 208 b of thesecond half-time-slot 202 b.

Re-Pointing Using a DRC Lock Indication—Introduction

[0063] A re-pointing decision is made by the AT 104 in accordance with acondition of a forward link, a condition of a reverse link, or acondition of both a forward link and a reverse link. As described above,the AT 104 determines a forward link quality metric directly, e.g., bymeasuring the forward link SINR. The quality metric of a reverse linkmay comprise a reverse link SINR, a DRC erasure rate, a filtered RPCmean, and other quality metrics known to one skilled in the art.

[0064] As discussed, the AT 104 identifies a serving sector of aparticular AP and transmits a DRC message on a DRC channel on a reverselink. The reverse link carrying the DRC messages between the AT 104 andthe serving sector is subject to various factors that changecharacteristics of the communication channel. In a wirelesscommunications systems these factors comprise, but are not limited to:fading, noise, interference from other terminals, and other factorsknown to one skilled in the art. The DRC message is protected againstthe changing characteristics of the communication channel by variousmethods, e.g., message length selection, encoding, symbol repetition,interleaving, transmission power, and other methods known to one ofordinary skill in the art. However, these methods impose performancepenalties, e.g., increased overhead, thus, decreased throughput,increased power consumption, increased peak-to-average power, increasedpower amplifier backoff, more expensive power amplifiers, and otherpenalties known to one skilled in the art. Therefore, an engineeringcompromise between a reliability of message delivery and an amount ofoverhead must be made. Consequently, even with the protection ofinformation, the conditions of the communication channel can degrade tothe point at which the serving sector possibly cannot decode (erases)some of the DRC messages. Therefore, the DRC erasure rate is directlyrelated to the conditions of the reverse link, and the DRC erasure rateis a good quality metric of the reverse link.

[0065] However, the AT 104 can directly determine neither the reverselink SINR nor the DRC erasure rate. Both the reverse link SIR and theDRC erasure rate may be directly determined by the sectors in the AT 104active set. The sector(s) then supplies the AT 104 with the determinedvalues of the reverse link SINR or the DRC erasure rate via a feedbackloop. In order for a sector to transmit accurate information regardingthe reverse link SINR or DRC erasure rate, the sector must use someforward link capacity. In order to minimize the impact on forward linkcapacity the reverse link SINR or the DRC erasure rate is sent with verylow granularity. In one embodiment, the granularity is one bit.Furthermore, a consideration of a feedback loop speed versus aperformance of the Reverse Link Traffic Channel performance must bemade.

[0066] Therefore, in a Message Based DRC Lock embodiment, each sector inthe AT 104 active set monitors the DRC channel and evaluates an erasurerate of the DRC messages. Each sector then sets a DRC Lock Bit for theAT 104 in accordance with the evaluated erasure rate. In one embodiment,the DRC Lock Bit set to one value, e.g., one (“in-lock”), indicates thatthe DRC erasure rate is acceptable; the DRC Lock Bit set to a secondvalue, e.g., zero (“out-of-lock”), indicates that the DRC erasure rateis unacceptable. The serving sector then sends the DRC Lock Bit to theAT 104 in a message on a control channel. The control channel for acommunication system in accordance with the IS-856 standard has a periodof 426 ms.

[0067] In a Punctured DRC Lock embodiment, the DRC Lock Bit is updatedat a rate different from the control channel period and punctured intoan RPC channel one or more times every frame. The term punctured is usedherein to mean sending the DRC Lock Bit instead of a RPC bit.

[0068] The AT 104 then uses the reverse link quality metric togetherwith the forward link quality metric to make a re-pointing decision.

Re-Pointing with a Message Based DRC Lock Access Point Processing

[0069] The processing method at the AP in accordance with one embodimentcomprises there phases. In the first phase, mapping a DRC Erasure and/ora valid DRC to a binary form generates a DRC Erasure Bit. In the secondphase, processing the DRC Erasure Bits generates a DRC erasure rate. Inthe third phase, sampling the processed DRC erasure rate every controlchannel period generates a DRC Lock Bit.

[0070] The above-described phases one and two are repeated everytime-slot by every sector in the AT 104 active set, as illustrated inFIG. 3 in accordance with an embodiment. The method starts in step 302.The method continues in step 304.

[0071] In step 304, the AP receives an updated DRC. The method continuesin step 306.

[0072] In step 306, the AP tests the updated DRC. If the DRC was erased,the method continues in step 308, otherwise, the method continues instep 310.

[0073] In step 308, the DRC Erasure Bit is assigned a value of one. Themethod continues in step 312.

[0074] In step 310, the DRC Erasure Bit is assigned a value of zero. Themethod continues in step 312.

[0075] In step 312, the DRC Erasure Bit is processed to generate a DRCerasure rate.

[0076] In one embodiment, the processing comprises filtering by a filterwith a pre-determined time constant. In one embodiment, the filter isrealized in a digital domain. The value of the pre-determined timeconstant may be established in accordance with system simulation, byexperiment or via other engineering methods known to one of ordinaryskills in the art as an optimum in accordance with:

[0077] reliability of an estimate ensuing from a choice of the timeconstant, and

[0078] latency of an estimate ensuing from the choice of the timeconstant.

[0079] The method continues in step 314.

[0080] In step 314, the system time is tested to establish the beginningof a control channel capsule. If the test is positive, the methodcontinues in step 316, otherwise the method returns to step 304.

[0081] Steps 316 through 326 introduce hysteresis rules for generatingthe DRC Lock Bit. The hysteresis is introduced to avoid rapidre-pointing when the channel SINR varies rapidly. The hysteresis rulesare as follows:

[0082] If the DRC Lock Bit is currently set to one, then the filteredDRC erasure rate must exceed first DRC erasure threshold(DRC_ErasureTh2) for the DRC Lock Bit to be set to zero.

[0083] If the DRC Lock Bit is currently set to zero, then the FilteredDRC Erasure rate has to be below a second pre-determined DRC erasurethreshold (DRC_Erasure_Th1) for the DRC Lock to be set to one.

[0084] In one embodiment, the values DRC_Erasure_Th1 and DRC_Erasure_Th2are pre-determined in accordance with the communication systemsimulation, by experiment or other engineering methods known to one ofordinary skills in the art. In another embodiment, the valuesDRC_Erasure_Th1 and DRC_Erasure_Th2 are changed in accordance with thechange of the conditions of the communication link. In eitherembodiment, the values of DRC_Erasure_Th1 and DRC_Erasure_Th2 areselected to optimize the following requirements to:

[0085] minimize the dead-zone (when the DRC Lock Bit is not updated);and

[0086] transmit the most current reverse link channel state informationto the AT.

[0087] In step 316, the current DRC Lock Bit value is compared to 1. Ifthe DRC Lock Bit value equals 1, the method continues in step 320;otherwise, the method continues in step 318.

[0088] In step 318, the DRC erasure rate is compared to theDRC_Erasure_Th1. If the DRC erasure rate is less than theDRC_Erasure_Th1, the method continues in step 322; otherwise, the methodcontinues in step 324.

[0089] In step 320, the DRC erasure rate is compared to theDRC_Erasure_Th2. If the DRC erasure rate is less than theDRC_Erasure_Th2, the method continues in step 324; otherwise, the methodcontinues in step 326.

[0090] In step 322, the DRC Lock Bit value is set to 0. The methodcontinues in step 328.

[0091] In step 324, the DRC Lock Bit value is set to 1. The methodcontinues in step 328.

[0092] In step 326, the DRC Lock Bit value is set to 0. The methodcontinues in step 328.

[0093] In step 328, the DRC Lock Bit is set at the appropriate positionof the control channel message. The method returns to step 304.

Access Terminal Processing

[0094] As discussed, in one embodiment, the AT is assumed to be able todemodulate a control channel from only one sector in the AT's activeset. The processing method at the AT in accordance with the embodimentcomprises the phases of (i) Initialization, (ii) Credit Accumulation,and (iii) Decision.

Initialization

[0095] During the initialization stage, the AT 104 selects a sector withthe best forward link quality metric, i.e., the highest SINR, as theserving sector. The AT 104 sets the DRC for the selected sector“in-lock” and initializes credits for all non-serving sectors to zero.

[0096] In one embodiment, two types of credits are defined—switchingcredits and monitoring credits. The credits are described in moredetails in the Credit Accumulation paragraph.

[0097] The initialization phase in accordance with one embodiment isillustrated in FIG. 4. The method starts in step 402. The methodcontinues in step 404.

[0098] In step 404, the AT selects a sector with the best forward linkquality metric as the serving sector, and sets the sector's DRC“in-lock.” The method continues in step 406.

[0099] In step 406, a variable count is set to one. The method continuesin step 408.

[0100] In step 408, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in an accumulation phase; otherwise, the methodcontinues in step 410.

[0101] In step 410, the inquiry is made whether the sector designated bythe variable count is the current serving sector as selected in step404. If the test is positive, the method continues in step 414;otherwise, the method continues in step 412.

[0102] In step 412, monitoring credits for a non-serving sector (CM_NS)and switching credits for a non-serving sector (CS_NS) are set to zero.The method continues in step 414.

[0103] In step 414, the variable count is incremented, and the methodreturns to step 408.

Credit Accumulation

[0104] As discussed, two types of credits are defined—switching creditsand monitoring credits in accordance with one embodiment. Switchingcredits are used to qualify a non-serving sector for re-pointing, if theDRC of the non-serving sector is “in lock” with a pre-determinedprobability. Thus, CS_NS are incremented if:

[0105] a forward link SINR of the non-serving sector (FL_NS) is greaterthan a forward link SINR of the current serving sector (FL_SS) modifiedby a pre-determined value (FL_SINR_Th); and

[0106] a filtered RPC mean for the non-serving sector (RL_NS) is below apre-determined threshold (RPC_Th).

[0107] CS_NS are decremented if the above conditions are not satisfied.

[0108] The pre-determined value FL_SINR_Th is selected so thatre-pointing to another sector results in an increase in forward linkSINR and, consequently, in an increase in an average requested datarate.

[0109] The pre-determined threshold RPC_Th is chosen so that the AP'sDRC is “in-lock” with a probability PIL when the filtered RPC mean isbelow the RPC_Th. The relationship between the probability PIL and thethreshold is determined in accordance with simulations, laboratorytests, field trails, and other engineering methods. The RPC_Th is chosento be conservative to minimize the cost associated with re-pointing theDRC to a sector with the DRC “out-of-lock.” If the AT did re-point to asector with the DRC “out-of-lock,” not only would the AT experiencedegraded throughput, but also a higher outage probability. The methodcan afford to select the RPC_Th conservatively because the monitoringcredits are used to re-point to sectors with filtered RPC mean greaterthan the threshold but with DRC ‘in-lock.” In one embodiment, the RPC_This chosen such that there is a less than 1% probability that the DRC is“out-of-lock” when the filtered RPC Mean is below the RPC_Th for anygiven channel conditions.

[0110] In one embodiment, the minimum value for the credits (bothswitching and monitoring) is zero, and the maximum for the credits isequal to a soft handoff delay or a softer handoff delay. The delay usedis determined based on whether or not the non-serving sector is in thesame cell as the serving sector. If the non-serving sector is in thesame cell as the serving sector, then the softer handoff delay is used,and if the non-serving serving sector is in a cell different from theone that the serving sector is part of, then the soft-handoff delay isused.

[0111] It is possible that a filtered RPC mean for the non-servingsector is above RPC_Th, and the DRC is “in-lock” for the non-servingsector. Considering the rules for incrementing the switching credits,the switching credits will not be incremented, although a forward linkSINR of the non-serving sector is greater than a forward link SINR ofthe current serving sector by FL_SINR_Th. Consequently, a throughput ofthe system is not optimized. In such a scenario, the AT uses themonitoring credits to determine whether to monitor control channels of anon-serving sector to determine whether the DRC Lock for the non-servingsector is “in-lock.” Therefore, the monitoring credits for a non-servingsector (CM_NS) are incremented if:

[0112] the forward link SINR of the non-serving sector (FL_NS) isgreater than the forward link SINR of the current serving sector (FL_SS)by a FL_SINR_Th; and

[0113] the filtered RPC mean for the non-serving sector (RL_NS) is abovethe RPC_Th; and

[0114] the filtered RPC mean for the current serving sector (RL_SS) isbelow the RPC_Th.

[0115] CM_NS are decremented if the above conditions are not satisfied.

[0116] The credits, initialized to zero in the Initialization phase, areaccumulated during the Credit Accumulation phase. The creditaccumulation phase, in accordance with one embodiment, is illustrated inFIG. 5. In step 502, a variable count is set to one. The methodcontinues in step 504.

[0117] In step 504, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in decision phase;

[0118] otherwise, the method continues in step 506.

[0119] In step 506, the inquiry is made whether a sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 518; otherwise, the methodcontinues in step 508.

[0120] In step 508, a forward link SINR of a sector designated by thevariable count is compared against forward link SINR of the currentserving sector modified by the FL_SINR_Th. If the forward link SINR ofthe sector designated by the variable count is greater than the forwardlink SINR of the current serving sector modified by the FL_SINR_Th, themethod continues in step 510; otherwise, the method continues in step512.

[0121] In step 510, a reverse link filtered RPC mean of the sectordesignated by the variable count is compared against the RPC_Th. If thereverse link filtered RPC mean of the sector designated by the variablecount is greater than the RPC_Th, the method continues in step 511;otherwise, the method continues in step 516.

[0122] In step 511, a reverse link filtered RPC mean for the currentserving sector is compared against the RPC_Th. If the reverse linkfiltered RPC mean for the current serving sector is greater than theRPC_Th, the method continues in step 512; otherwise, the methodcontinues in step 514.

[0123] In step 512, values of CS_NS and CM_NS identified by the variablecount are decremented by one, and set to the maximum of 0 and thedecremented value. The method continues in step 518.

[0124] In step 514, the values of CS_NS and CM_NS identified by thevariable count are incremented by one and set to the minimum of the soft(or softer) handoff delay (NS_S_Th) and the incremented value. Themethod continues in step 518.

[0125] In step 516, the value of CS_NS identified by the variable countis incremented by one, and set to the minimum of the soft (or softer)handoff delay (NS_S_Th) and the decremented value. The method continuesin step 518.

[0126] In step 518, the variable count is incremented by one and themethod returns to step 504.

Decision

[0127] In one embodiment, the re-pointing decision rules depend on theDRC Lock Bit of the current serving sector. Consequently, referring toFIG. 6, in step 602, a DRC Lock Bit of the current serving sector istested. If the DRC Lock Bit of the current serving sector is“out-of-lock,” the method continues in step 604; otherwise, the methodcontinues in step 606.

[0128] In step 604, the “out-of-lock” server selection method isinitialized. The method is described in detail with reference to FIG. 9.The method returns to the credit accumulation phase.

[0129] In step 606, the “in-lock” server selection method isinitialized. The method is described in detail with reference to FIGS. 7and 8. The method returns to the credit accumulation phase.

“In-Lock” Server Selection

[0130] If the DRC Lock Bit from the current serving sector is “in-lock”,the decision to re-point to a non-serving sector is made if thenon-serving sector provides higher FL_SINR and an “in-lock” DRC LockBit. To carry out the decision, the AT first ascertains if any of thenon-serving sectors has switching credits greater than a thresholddetermined by the soft/softer delay. (This, threshold is the same forboth the switching and monitoring credits.) If at least one of thenon-serving sectors has switching credits greater than the threshold,the AT re-points its DRC to the sector with the highest switchingcredits. In one embodiment, if two or more non-serving sectors haveequal switching credits, the sector with the highest quality reverselink is selected. The quality of the reverse link is determined inaccordance with the filtered RPC mean. Lower filtered RPC mean indicatesa better quality of the reverse link. In another embodiment, if two ormore non-serving sectors have equal switching credits, the sector withthe highest quality forward link is selected.

[0131] If none of the non-serving sectors has sufficient switchingcredits to mandate re-pointing, the AT ascertains how many of thenon-serving sectors have monitoring credits greater than the threshold.If at least one of the non-serving sectors has monitoring creditsgreater than the threshold, the AT monitors the control channel fromthose non-serving sectors during the next control channel cycle. In oneembodiment, if two or more non-serving sectors have equal switchingcredits, a sector with the highest quality reverse link is selected forthe monitoring. The quality of the reverse link is determined inaccordance with the filtered RPC mean. In another embodiment, if two ormore non-serving sectors have equal switching credits, a sector with thehighest quality forward link is selected for the monitoring. If the DRCfor the monitored sector is “in-lock,” the AT re-points to the monitoredsector. Following the re-pointing the AT resets all the switching andmonitoring credits.

[0132] If none of the non-serving sectors has either sufficientswitching credits or monitoring credits, the AT continues pointing itsDRC to the current serving Access Point.

[0133] The decision phase in accordance with one embodiment isillustrated in FIGS. 7 and 8. In accordance with FIG. 7, a non-servingsector is made a candidate for re-pointing if the non-serving sector'sswitching credits are equal to the soft (or softer) handoff delay(NS_S_Th) for the non-serving sector. A non-serving sector is made acandidate for a control channel monitoring if the non-serving sector'smonitoring credits are equal to the soft (or softer) handoff delay(NS_S_Th) for the non-serving sector and the filtered RPC mean of thenon-serving sector is above RPC_Th. This ensures that the AT is inreliable communication with the current serving sector when it attemptsto demodulate the synchronous control channel from a non-serving sector.These two requirements ensure that the DRC from the non-serving sectoris “in-lock” with a probability PIL.

[0134] Furthermore, in one embodiment, a data packet may span twocontrol channel cycles and, consequently, the data transmission from thecurrent serving sector may collide with the control channel transmissionfrom the sector to be monitored.

[0135] Consequently, the AT further determines whether there ispotential for a collision between the data on the control channel to bemonitored and the data form the current serving sector. If the ATdetermines that the data transmission from the current serving sectorwould collide with the transmission of the control channel from thenon-serving sector to be monitored, then the AT does not monitor thecontrol channel from the non-serving sector. Otherwise, the AT wouldmonitor the control channel from the non-serving sector.

[0136] In step 702, a variable count is set to one. The method continuesin step 704.

[0137] In step 704, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in server selection of FIG. 8; otherwise, the methodcontinues in step 706.

[0138] In step 706, an inquiry is made whether a sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 722;

[0139] otherwise, the method continues in step 708.

[0140] In step 708, a value of the variable CS_NS identified by thevariable count is compared against the soft (or softer) handoff delay(NS_S_Th) for the non-serving sector. If the value of the variable CS_NSis not equal to the NS_S_Th, the method continues in step 710;otherwise, the method continues in step 712.

[0141] In step 710, a value of the variable Cand_S identified by thevariable count is set to 0. The method continues in step 714.

[0142] In step 712, a value of the variable Cand_S identified by thevariable count is set to 1. The method continues in step 714.

[0143] In step 714, a value of the variable CM_NS identified by thevariable count is compared against the soft (or softer) handoff delay(NS_S_Th) for the non-serving sector. If the value of the variable CS_NSis not equal to the NS_S_Th for the non-serving sector, the methodcontinues in step 716; otherwise, the method continues in step 720.

[0144] In step 716, the filtered RPC mean of the current serving sector(RPC_CS) identified by the variable count is compared against an RPCthreshold (RPC_Th). If the RPC_CS is less than the RPC_Th, the methodcontinues in step 718; otherwise, the method continues in step 720.

[0145] In step 718, the AT determines whether the data on the controlchannel to be monitored and the data from the current serving sectorcollide. If the AT determines that the data transmission from thecurrent serving sector would collide with the transmission of thecontrol channel from the non serving sector to be monitored, then themethod continues in step 720. Otherwise, the method continues in step722.

[0146] In step 720, a value of the variable Cand_M identified by thevariable count is set to 0. The method continues in step 724.

[0147] In step 722, a value of the variable Cand_M identified by thevariable count is set to 1. The method continues in step 724.

[0148] In step 724, the variable count is incremented, and the methodreturns to step 704.

[0149] Referring to FIG. 8, the “in-lock” selection from FIG. 7continues. In accordance with FIG. 8, the AT ascertains which sectorsare candidates for re-pointing and/or monitoring, and carries out there-pointing decision.

[0150] In step 802, where a variable count is set to one, the methodcontinues in step 804, in which the variable count is tested against anactive set size. If the variable count is greater than the active setsize, the method continues in step 814; otherwise, the method continuesin step 806.

[0151] In step 806, an inquiry is made whether the sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 812; otherwise, the methodcontinues in step 808.

[0152] In step 808, a variable Cand_S identified by the variable countis compared to one. If the variable Cand_S identified by the variablecount is equal to one, the method continues in step 810; otherwise themethod continues in step 812.

[0153] In step 810, a variable CS_NS_count is incremented by one. Themethod continues in step 812.

[0154] In step 812, the variable count is incremented, and the methodreturns to step 804.

[0155] In step 814, the value of the variable CS_NS_count isascertained. If the value of the variable CS_NS_count is equal to 1, themethod continues in step 816. If the value of the variable CS_NS_countis greater that 1, the method continues in step 818. Otherwise, themethod continues in step 822.

[0156] In step 816, the AT re-points the DRC to the candidate sectoridentified by the variable count. The method continues in step 820.

[0157] In step 818, the AT re-points the DRC to the candidate sectoridentified by the variable count that has the highest quality reverselink in accordance with the sector's reverse link's filtered RPC mean.The method continues in step 820.

[0158] In step 820, the variables CS_NS and the variables CM_NS are setto zero. The method returns to the credit accumulation phase.

[0159] In step 822, a variable count is set to one. The method continuesin step 824.

[0160] In step 824, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in step 834; otherwise, the method continues in step826.

[0161] In step 826, an inquiry is made whether the sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 832; otherwise, the methodcontinues in step 828.

[0162] In step 828, a variable Cand_M identified by the variable countis compared to one. If the variable Cand_M identified by the variablecount is equal to one, the method continues in step 830; otherwise themethod continues in step 832.

[0163] In step 830, a variable CM_NS_count is incremented. The methodcontinues in step 832.

[0164] In step 832, the variable count is incremented, and the methodreturns to step 824.

[0165] In step 834, the value of the variable CM_NS_count isascertained. If the value of the variable CM_NS_count is equal to 1, themethod continues in step 836. If the value of the variable CM_NS_countis greater that 1, the method continues in step 838. If the value of thevariable CM_NS_count is equal to 0, the method continues in step 840.

[0166] In step 836, the AT monitors the DRC from the candidate sectoridentified by the variable count. The method continues in step 842.

[0167] In step 838, the AT monitors the DRC from the candidate sectoridentified by the variable count that has the highest quality reverselink in accordance with the AP's reverse link's filtered RPC mean. Themethod continues in step 842.

[0168] In step 840, the AT makes the-decision not to re-point to adifferent sector. The method returns to credit accumulation.

[0169] In step 842, the DRC from the candidate sector is evaluated. Ifthe DRC value is “in lock,” the method continues in step 844; otherwise,the method returns to credit accumulation.

[0170] In step 844, the AT re-points the DRC to the candidate sector.The method continues in step 846.

[0171] In step 846, the variables CS_NS and the variables CM_NS are setto zero. The method returns to credit accumulation.

“Out-of-Lock” Server Selection

[0172] If the DRC from the current serving sector is “out-of-lock,” thedecision to re-point to a non-serving sector is made if the non-servingsector provides higher FL_SINR and better quality reverse link, asdetermined by the switching credits. To carry out the decision, the ATfirst ascertains those non-serving sectors that have switching creditsgreater than zero. If at least one of the non-serving sectors hasswitching credits greater than zero, the AT re-points the DRC to thesector with the highest switching credits. In one embodiment, if two ormore non-serving sectors have equal switching credits, a sector with thehighest quality reverse link is selected. The quality of the reverselink is determined in accordance with the reverse link's filtered RPCmean. In another embodiment, if two or more non-serving sectors haveequal switching credits, a sector with the highest quality forward linkis selected.

[0173] If none of the non-serving sectors has switching credits greaterthan zero, the AT ascertains those non-serving sectors that havemonitoring credits greater than zero. If at least one of the non-servingsectors has monitoring credits greater than zero, the AT monitors thesector with the highest monitoring credits. In one embodiment, if two ormore non-serving sectors have equal monitoring credits, the sector withthe highest quality reverse link is selected for the monitoring. Thequality of the reverse link is determined in accordance with thefiltered RPC mean. In another embodiment, if two or more non-servingsectors have equal monitoring credits, the sector with the highestquality forward link is selected for the monitoring. If the DRC for themonitored sector is “in-lock,” the AT re-points to the monitored sector.On re-pointing the DRC the AT resets all the switching and re-pointingcredits.

[0174] If none of the non-serving sectors has either sufficientswitching credits or monitoring credits, the AT continues pointing itsDRC to the current serving sector.

[0175] The “out-of-lock” sector selection in accordance with oneembodiment is illustrated in FIG. 9. In step 902, a variable CM_NS_countis set to zero. The method continues in step 904.

[0176] In step 904, the variable count is set to one. The methodcontinues in step 906.

[0177] In step 906, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in step 916; otherwise, the method continues in step908.

[0178] In step 908, an inquiry is made whether the sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 914; otherwise, the methodcontinues in step 910.

[0179] In step 910, a variable CS_NS identified by the variable count iscompared to zero. If the variable CS_NS identified by the variable countis equal to zero, the method continues in step 912; otherwise the methodcontinues in step 914.

[0180] In step 912, a variable CS_NS_count is incremented. The methodcontinues in step 914.

[0181] In step 914, the variable count is incremented, and the methodreturns to step 906.

[0182] In step 916, the value of the variable CS_NS_count isascertained. If the value of the variable CS_NS_count is equal to 1, themethod continues in step 918. If the value of the variable CS_NS_countis greater that 1, the method continues in step 920. Otherwise, themethod continues in step 922.

[0183] In step 918, the AT re-points the DRC to the candidate sectoridentified by the variable count. The method continues in step 944.

[0184] In step 920, the AT re-points the DRC to the candidate sectoridentified by the variable count that has the highest quality reverselink in accordance with the AP's reverse link's filtered RPC mean. Themethod continues in step 944.

[0185] In step 922, a variable CM_NS_count is set to zero. The methodcontinues in step 924.

[0186] In step 924, a variable count is set to one. The method continuesin step 926.

[0187] In step 926, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in step 936, otherwise, the method continues in step928.

[0188] In step 928, an inquiry is made whether the sector designated bythe variable count is the current serving sector. If the test isnegative, the method continues in step 934; otherwise, the methodcontinues in step 930.

[0189] In step 930, a variable CM_NS identified by the variable count iscompared to zero. If the variable CM_NS identified by the variable countis less than zero, the method continues in step 934; otherwise themethod continues in step 932.

[0190] In step 932, a variable CM_NS_count is incremented. The methodcontinues in step 934.

[0191] In step 934, the variable count is incremented, and the methodreturns to step 924.

[0192] In step 936, the value of the variable CM_NS_count isascertained. If the value of the variable CM_NS_count is equal to 1, themethod continues in step 938. If the value of the variable CM_NS_countis greater that 1, the method continues in step 940. If the value of thevariable CM_NS_count is equal to 0, the method continues in step 942.

[0193] In step 938, the AT re-points the DRC to the candidate sectoridentified by the variable count. The method continues in step 944.

[0194] In step 940, the AT re-points the DRC to the candidate sectoridentified by the variable count that has the highest quality reverselink in accordance with the AP's reverse link's filtered RPC mean. Themethod continues in step 944.

[0195] In step 942, the AT makes the decision not to re-point to adifferent sector. The method returns to credit accumulation.

Access Terminal Processing

[0196] In another embodiment, the AT is assumed to be able to demodulatea control channel from each sector in the AT's active set. Theprocessing method at the AT in accordance with the embodiment comprisesthe phases of (i) Initialization, (ii) Credit Accumulation, and (iii)Decision.

Initialization

[0197] During the initialization stage, the AT 104 selects the AP withthe best forward link quality metric, i.e., the highest SINR. The AT 104sets the DRC “in-lock,” for the selected AP. The AT 104 then initializescredits for all non-serving sectors to zero.

[0198] Because the AT is able to demodulate a control channel from eachsector in the AT's active set, thus determining the DRC Lock Bit value,there is no need for monitoring credits and only switching credits aredefined. The switching credits are described in more details in theCredit Accumulation paragraph. Consequently, the initialization phase inaccordance with the embodiment is carried out according to FIG. 4 andthe accompanying text, except for step 412. In step 412, only theswitching credits for a non-serving sector (CS_NS) are set to zero.

Credit Accumulation

[0199] As discussed, only switching credits are required in accordancewith the embodiment. Switching credits are used to qualify thenon-serving sector for re-pointing if the DRC of the non-serving sectoris “in lock.” Consequently, CS_NS are incremented if:

[0200] a forward link SINR of the non-serving sector (FL_NS) is greaterthan a forward link SINR of the current serving sector by apre-determined value (FL_SINR_Th); and

[0201] a DRC Lock Bit of the non-serving sector is “in-lock.”

[0202] The pre-determined value FL_SINR_Th is selected so thatre-pointing to a new sector results in an increase in forward link SINRand, consequently, in an increase in an average requested data rate.CS_NS are decremented if the above conditions are not satisfied.

[0203] In one embodiment, the switching credits minimum value is zeroand the maximum value is equal to a soft handoff delay if re-pointing tothe particular sector would constitute a soft handoff, or a softerhandoff delay if re-pointing to the particular AP would constitute asofter handoff.

[0204] The credits, initialized to zero in the Initialization phase areaccumulated during the Credit Accumulation phase. The creditaccumulation phase in accordance with one embodiment is illustrated inFIG. 10. In step 1002, a variable count is set to one. The methodcontinues in step 1004.

[0205] In step 1004, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in decision phase; otherwise, the method continues instep 1006.

[0206] In step 1006, the inquiry is made whether the sector designatedby the variable count is the current serving sector. If the test ispositive, the method continues in step 1016; otherwise, the methodcontinues in step 1008.

[0207] In step 1008, a forward link SINR of the sector designated by thevariable count is compared against forward link SINR of the currentserving sector modified by the FL_SINR_Th. If the forward link SINR ofthe sector designated by the variable count is greater than the forwardlink SINR of the current serving sector modified by the FL_SINR_Th, themethod continues in step 1010; otherwise, the method continues in step1012.

[0208] In step 1010, a DRC Lock Bit of the sector designated by thevariable count is compared against one. If the DRC Lock Bit of thesector designated by the variable count is equal to one, the methodcontinues in step 1014; otherwise, the method continues in step 1012.

[0209] In step 1012, the value of CS_NS identified by the variable countis decremented by one and set to the maximum of 0 and the decrementedvalue. The method continues in step 1016.

[0210] In step 1014, the value of CS_NS identified by the variable countare incremented by one and set to the minimum of the soft (or softer)handoff delay and the incremented value. The method continues in step1016.

[0211] In step 1016, the variable count is incremented by one and themethod returns to step 1004.

Decision

[0212] In accordance with the embodiment, the re-pointing decision rulesdepend on the DRC Lock State of the current serving sector.Consequently, the decision phase in accordance with the embodiment iscarried out according to FIG. 6 and accompanying text.

“In-Lock” AP Selection

[0213] If the DRC from the current serving sector is “in-lock,” thedecision to re-point to a non-serving sector is made if the non-servingsector provides higher FL_SINR and an “in-lock” DRC. To carry out thedecision, the AT first ascertains if any of the non-serving sectors hasswitching credits greater than a threshold determined by the soft/softerdelay. If at least one of the non-serving sectors has switching creditsgreater than the threshold, the AT re-points its DRC to the AP with thehighest switching credits. In one embodiment, if two or more non-servingsectors have equal switching credits, a sector with the highest qualityreverse link is selected. The quality of the reverse link is determinedin accordance with the filtered RPC mean. In another embodiment, if twoor more non-serving sectors have equal switching credits, a sector withthe highest quality forward link is selected.

[0214] To avoid limiting the re-pointing rate to a control channelinterval (256 time-time-slots for IS-856), a non-serving sector isfurther made a candidate for re-pointing between control channelintervals according to the following rules:

[0215] the number of time-slots since the last control channel (CC)exceeds a threshold N_(c); and

[0216] the filtered RPC mean for the non-serving sector (RL_NS) is lessthan the RPC_Th.

[0217] The RPC_Th is chosen such that the DRC for the non-serving sectoris “in-lock” with a probability PIL if the filtered RPC mean is belowRPC_Th. In one embodiment, the Nc is equal to 64.

[0218] If none of the non-serving sectors has sufficient switchingcredits, the AT continues pointing its DRC to the current servingsector. On re-pointing the DRC the AT resets all the switching credits.

[0219] The candidate determination in accordance with the embodiment isillustrated in FIG. 11. In step 1102, a variable count is set to one.The method continues in step 1104.

[0220] In step 1104, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in server selection as described below; otherwise, themethod continues in step 1106.

[0221] In step 1106, an inquiry is made whether the sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 1118; otherwise, the methodcontinues in step 1108.

[0222] In step 1108, a value of the variable CS_NS identified by thevariable count is compared against the soft (or softer) handoff delay(NS_S_Th) for the non-serving sector. If the value of the variable CS_NSis not equal to the NS_S_Th for the non-serving sector, the methodcontinues in step 1110; otherwise, the method continues in step 1112.

[0223] In step 1110, a value of the variable identifying the number oftime-slots since the last control channel (CC) is compared against theNC. If the CC is greater than the Nc, the method continues in step 1114;otherwise, the method continues in step 1116.

[0224] In step 1112, a value of the variable Cand_S identified by thevariable count is set to zero. The method continues in step 1118.

[0225] In step 1114, a filtered RPC mean of the non-serving sector(RL_NS) identified by the variable count is compared against an RPCthreshold (RPC_Th). If the RL_NS is greater than the RPC_TH, the methodcontinues in step 1112; otherwise, the method continues in step 1116.

[0226] In step 1116, a value of the variable Cand_S identified by thevariable count is set to one. The method continues in step 1118.

[0227] In step 1118, the variable count is incremented, and the methodreturns to step 1104.

[0228] In accordance with the decision rules, the AT ascertains whichsectors are candidates for re-pointing, and carries out the re-pointingdecision. The decision phase in accordance with the embodiment iscarried out according to FIG. 9 and the accompanying text, with thefollowing modifications. Because the embodiment does not use themonitoring credits, steps 922 through 946 are deleted. Consequently, instep 914, if the value of the variable CS_NS_count is equal to zero, themethod continues pointing to the current serving Access Point, and thenreturns to the Credit Accumulation phase.

“Out-of-Lock” AP Selection

[0229] If the DRC from the current serving sector is “out-of-lock” thedecision to re-point to a non-serving sector is made if the non-servingsector provides higher FL_SINR and better quality reverse link, asdetermined by the switching credits. To carry out the decision, the ATfirst ascertains those non-serving sectors that have switching creditsgreater than zero. If at least one of the non-serving sectors hasswitching credits greater than zero, the AT re-points its DRC to thesector with the highest switching credits. In one embodiment, if two ormore non-serving sectors have equal switching credits, a sector with thehighest quality reverse link is selected. The quality of the reverselink is determined in accordance with the reverse link's filtered RPCmean. In another embodiment, if two or more non-serving sectors haveequal switching credits, a sector with the highest quality forward linkis selected.

[0230] If none of the non-serving sectors has sufficient switchingcredits, the AT continues pointing its DRC to the current serving AccessPoint.

[0231] The decision phase in accordance with the embodiment is carriedout according to FIG. 9 and the accompanying text, with the followingmodifications. Because the embodiment does not use the monitoringcredits, steps 922 through 946 are deleted. Consequently, in step 914,if the value of the variable CS_NS_count is equal to zero, the methodcontinues pointing to the current serving Access Point, and then returnsto the Credit Accumulation phase.

Further Extension

[0232] One skilled in the art recognizes that the concepts explained inthe two above-described embodiments can be utilized to devise a hybridmethod in which the AT would be able to demodulate a control channelfrom at least two sectors in the AT's active set. A modification to aCredit Accumulation phase as required in one embodiment is illustratedin FIG. 12. All other phases do not require any modifications.

[0233] In step 1210, the sectors control channels to be demodulated aredetermined. In one embodiment, the determination is carried out inaccordance with the sector's filtered forward link SINR. Sectors aresorted based on their filtered forward link SINR. Then the AT selectsthe number of sectors it is able to demodulate as the sectors with thehighest SINR.

[0234] In step 1212, a variable count is set to one. The methodcontinues in step 1214.

[0235] In step 1214, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in decision phase;

[0236] otherwise, the method continues in step 1216.

[0237] In step 1216, the inquiry is made whether a sector designated bythe variable count is the current serving sector. If the test ispositive, the method continues in step 1236; otherwise, the methodcontinues in step 1218.

[0238] In step 1218, a forward link SINR of a sector designated by thevariable count is compared against forward link SINR of the currentserving sector modified by the FL_SINR_Th. If the forward link SINR ofthe sector designated by the variable count is greater than the forwardlink SINR of the current serving sector modified by the FL_SINR_Th, themethod continues in step 1222; otherwise, the method continues in step1220.

[0239] In step 1220, a test whether a sector identified by the variablecount was selected for demodulating is performed. If the test isnegative, the method continues in step 1228; otherwise the methodcontinues in step 1234.

[0240] In step 1222, a test whether a sector identified by the variablecount was selected for demodulating is performed. If the test isnegative, the method continues in step 1224; otherwise the methodcontinues in step 1226.

[0241] In step 1224, a reverse link filtered RPC mean of the sectordesignated by the variable count is compared against the RPC_Th. If thereverse link filtered RPC mean of the sector designated by the variablecount is greater than the RPC_Th, the method continues in step 1225;otherwise, the method continues in step 1232.

[0242] In step 1225, a reverse link filtered RPC mean for the currentserving sector is compared against the RPC_Th. If the reverse linkfiltered RPC mean for the current serving sector is greater than theRPC_Th, the method continues in step 1228; otherwise, the methodcontinues in step 1230.

[0243] In step 1226, a DRC Lock of the sector identified by the variablecount is compared to one. If the DRC Lock of the sector identified bythe variable count is equal to one, the method continues in step 1232;otherwise the method continues in step 1234.

[0244] In step 1228, values of CS_NS and CM_NS identified by thevariable count are decremented by one, and set to the maximum of 0 andthe decremented value. The method continues in step 1236.

[0245] In step 1230, the values of CS_NS and CM_NS identified by thevariable count are incremented by one, and set to the minimum of thesoft (or softer) handoff delay (NS_S_Th) and the incremented value. Themethod continues in step 1236.

[0246] In step 1232, the value of CM_NS identified by the variable countis incremented by one and set to the minimum of the soft (or softer)handoff delay (NS_S_Th) and the decremented value. The method continuesin step 1236.

[0247] In step 1234, the value of CS_NS identified by the variable countis decremented by one, and set to the maximum of 0 and the decrementedvalue. The method continues in step 1236.

[0248] In step 1236, the variable count is incremented by one and themethod returns to step 1214.

Re-Pointing Using a Punctured DRC Lock

[0249] Depending on an implementation of a communication system, aperformance of the re-pointing method using a DRC Lock for indication ofa reverse link condition may suffer due to the delay in the feedbackloop. The update rate of the feedback loop may be too slow in handlingsudden changes in reverse link quality. Such performance detriment mayresult in outages, which may be intolerable in certain application,e.g., real-time applications.

[0250] Therefore, in another embodiment, the DRC Lock Bit is updated ata higher rate and punctured into an RPC channel one or more times everyframe. The term punctured is used herein to mean sending the DRC LockBit instead of a RPC bit. The DRC Lock Bit is sent by all the AP's inthe AT 104 active set. In one embodiment, a transmission of the DRC LockBit to each AT is staggered, i.e. referenced off a frame offset assignedto the AT. This allows for allocating additional power to the RPCchannel during the transmission of the DRC Lock Bit in order to providean additional margin to reduce the DRC Lock Bit errors at the AT;therefore, preventing an erroneous handoffs and possible loss in forwardlink throughput. The AT 104 uses the DRC Lock Bit information to selectthe serving AP.

Access Point Processing

[0251] The method in accordance with one embodiment is illustrated inFIG. 13. The method starts in step 1302. The method continues in step1304.

[0252] In step 1304, the AP receives an updated DRC. The methodcontinues in step 1306.

[0253] In step 1306, the AP tests the received DRC. If the DRC waserased, the method continues in step 1308; otherwise, the methodcontinues in step 1310.

[0254] In step 1308, the DRC erasure is assigned a value of 1. Themethod continues in step 1312.

[0255] In step 1310, the DRC erasure is assigned a value of 0. Themethod continues in step 1312.

[0256] In step 1312, the DRC Erasure Bit is processed to generate a DRCerasure rate. In one embodiment, the processing comprises filtering by afilter with a pre-determined time constant. In one embodiment, thefilter is realized in a digital domain. The value of the pre-determinedtime constant is established in accordance with system simulation, byexperiment or other engineering methods known to one of ordinary skillsin the art as an optimum in accordance with:

[0257] reliability of an estimate ensuing from a choice of the timeconstant, and

[0258] latency of an estimate ensuing from a choice of the timeconstant.

[0259] In one embodiment, pre-determined time constant is 64 time-slots.The method continues in step 1314.

[0260] In step 1314, the system time is tested to establish whether theDRC Lock Bit is to be punctured into the RPC sub channel. In oneembodiment, illustrated in step 1314, the DRC Lock Bit is punctured intothe RPC sub channel each eighth (mod 8) time instance. Because the aimof selecting the time instance is to achieve a pre determined bit errorrate, one of ordinary skills in the art recognizes that other timeinstances can be selected. The values of the time instance is selectedto optimize the following requirements:

[0261] Minimize the degradation of the reverse link resulting from lossof RPC bits due to puncturing; and

[0262] providing the DRC Lock Bit at optimal spacing.

[0263] If the test is positive, the method continues in step 1330;otherwise the method continues in step 1316.

[0264] In step 1316, the system time is tested to establish whether theDRC Lock Bit is to be updated. The time instance for the update isselected to ensure reliable delivery of the DRC Lock Bit. In oneembodiment, illustrated in step 1316, the DRC Lock Bit is updated everysixty-fourth (mod 64) time instance. If the test is positive, the methodcontinues in step 1318; otherwise the method returns to step 1304.

[0265] Steps 1318 through 1328 introduce hysteresis rules for generatingthe DRC Lock Bit. The hysteresis is introduced to avoid rapidre-pointing when the channel SINR varies rapidly. The hysteresis rulesare as follows:

[0266] If the DRC Lock Bit is currently set to one, then the filteredDRC erasure rate must exceed first DRC erasure threshold(DRC-Erasure_Th2) for the DRC Lock Bit to be set to zero; and

[0267] if the DRC Lock Bit is currently set to zero, then the FilteredDRC Erasure rate has to be below a second pre-determined DRC erasurethreshold (DRC_Erasure_Th1) for the DRC Lock to be set to one.

[0268] In one embodiment, the values DRC_Erasure_Th1 and DRC_Erasure_Th2are pre-determined in accordance with the communication systemsimulation by experiment or other engineering methods known to one ofordinary skills in the art. In another embodiment, the valuesDRC_Erasure_Th1 and DRC_Erasure_Th2 are changed in accordance with thechange of the conditions of the communication link. In eitherembodiment, the values of DRC_Erasure_Th1 and DRC_Erasure_Th2 areselected to optimize the following requirements:

[0269] minimize the dead-zone (when the DRC Lock Bit is not updated);and

[0270] transmit the most current reverse link channel state informationto the AT.

[0271] In step 1318, the DRC Lock Bit value is compared to 1. If the DRCLock Bit value equals 1, the method continues in step 1322; otherwise,the method continues in step 1320.

[0272] In step 1320, the DRC erasure rate is compared to theDRC_Erasure_Th1. If the DRC erasure rate is greater than theDRC_Erasure_Th1, the method continues in step 1324; otherwise, themethod continues in step 1326.

[0273] In step 1322, the DRC erasure rate is compared to theDRC_Erasure_Th2. If the DRC erasure rate is less than theDRC_Erasure_Th2, the method continues in step 1326; otherwise, themethod continues in step 1328.

[0274] In step 1324, the DRC Lock Bit value is set to 0. The methodcontinues in step 1330.

[0275] In step 1326, the DRC Lock Bit value is set to 1. The methodcontinues in step 1330.

[0276] In step 1328, the DRC Lock Bit value is set to 0. The methodcontinues in step 1330.

[0277] In step 1330, the DRC Lock Bit is punctured into the RPC channelin accordance with the timing signal obtained in step 1314. The methodreturns to step 1304.

Access Terminal Processing

[0278] The AT 104 receives and demodulates the RPC channel from all APsin the AT 104 active set. Consequently, the AT 104 recovers the DRC LockBits punctured into the RPC channel for every AP in the AT 104 activeset. Furthermore, as discussed, the punctured DRC Lock Bits are updatedwith a higher frequency than the Message Based DRC Lock Bits.Consequently, in a Demodulation phase, the AT 104 can combine the energyof received DRC Lock Bits during one update interval, and compare thecombined DRC Lock Bits energy against a DRC Lock Bit threshold. If thecombined DRC Lock Bit energy is greater than the DRC Lock Bit threshold,the AT 104 declares the DRC Lock Bit from the particular AP “in-lock.”In the Decision phase, the AT 104 uses the DRC Lock Bit value to make are-pointing decision.

Demodulation Phase

[0279] The Demodulation phase in accordance with one embodiment isillustrated in FIG. 14. The method starts in step 1402 and continues instep 1404.

[0280] In step 1404, the system time is tested to establish whether theDRC Lock Bit was updated. In one embodiment, illustrated in step 1404,the DRC Lock Bit is updated every sixty-fourth (mod 64) time instance.This time instance corresponds to the update rate at the AP. If the testis positive, the method continues in step 1410; otherwise the methodreturns to step 1406.

[0281] In step 1406, the system time is tested to establish whether theDRC Lock Bit was punctured into the RPC sub channel. In one embodiment,illustrated in step 1404, the DRC Lock Bit is punctured into the RPC subchannel each eighth (mod 8) time instance. This time instancecorresponds to the puncture rate at the AP. If the test is positive, themethod continues in step 1408; otherwise the method returns to step1404.

[0282] In step 1410, the combined DRC Lock Bit energy is tested againsta DRC Lock Bit threshold (DRC_LB_TH). If the test is positive, themethod continues in step 1412;

[0283] otherwise the method returns to step 1414.

[0284] In step 1412, the DRC Lock Bit value is set to 1. The methodcontinues in step 1416.

[0285] In step 1414, the DRC Lock Bit value is set to 0. The methodcontinues in step 1416.

[0286] In step 1416, the variable containing the combined DRC Lock Bitenergy is set to zero for the next update.

Decision Phase

[0287] The AT uses the DRC Lock Bit value obtainer in the Demodulationphase to make a decision with respect to a re-pointing. In oneembodiment, the decision phase comprises (i) Accreditation phase, (ii)Certification phase, and (iii) Decision phase. The respective phases aredescribed below.

Accreditation Phase

[0288] In the accreditation phase, the forward link SINR of thenon-serving sectors (FL_NS) is compared to the forward link SINR of thecurrent serving sector modified by a pre-determined hysteresis margin(FL_HYST). If the forward link SINR of the non-serving sector is greaterthan the forward link SINR of the serving sector modified by apre-determined hysteresis margin, then the temporary credits(TEMP_CREDIT) associated with that non-serving sector are incremented;otherwise, the temporary credits associated with that non-serving sectorare decremented.

[0289] The Accreditation phase in accordance with one embodiment isillustrated in FIG. 15. The method starts in step 1502. The methodcontinues in step 1504.

[0290] In step 1504, a variable count is set to zero. The methodcontinues in step 1506.

[0291] In step 1506, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in the Certification phase; otherwise, the methodcontinues in step 1508.

[0292] In step 1508, an inquiry is made whether the forward link SIR ofthe sector designated by the variable count is greater than the forwardlink SINR of the current serving sector modified by a pre-determinedhysteresis margin. If the test is positive, the method continues in step1512; otherwise, the method continues in step 1510.

[0293] In step 1510, the temporary credits for the sector identified bythe variable count are decreased by one. The method continues in step1514.

[0294] In step 1512, the temporary credits for the sector identified bythe variable count are increased by one. The method continues in step1514.

[0295] In step 1514, the variable count is increased by one. The methodreturns to step 1506.

Certification Phase

[0296] In the certification phase, the credits of the sectors arecertified. The term certification as used herein means a decision, whichsectors' credits (CREDITS) will be increased by the temporary creditsaccumulated by the sector during the accreditation phase. In oneembodiment, the certification decision is made in accordance with thefollowing rules:

[0297] If the DRC Lock Bit of the current serving sector is “in-lock,”and if the DRC Lock Bit on a non-serving sector is “in-lock,” then thecredits of the non-serving sector are incremented by the DRC LockInterval. The term DRC Lock interval as used herein means a number oftime-slots over which the DRC Lock Indication has been sent;

[0298] if the DRC Lock Bit of the current serving sector is“out-of-lock”, and if the DRC Lock Bit on a non-serving sector is“in-lock” then the credits of the non-serving sector are incremented bythe number of accumulated temporary credits;

[0299] otherwise the credits of the non-serving sector are set to zero.

[0300] The Certification phase in accordance with one embodiment isillustrated in FIG. 16. The method starts in step 1602, in which avariable count is set to zero. The method continues in step 1604.

[0301] In step 1604, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in the Decision phase; otherwise, the method continuesin step 1606.

[0302] In step 1606, the DRC_LOCK of the serving sector is comparedto 1. If the DRC_LOCK is equal to 1, the method continues in step 1610;otherwise, the method continues in step 1608.

[0303] In step 1608, the DRC_LOCK of the non-serving sector identifiedby the variable count is compared to 1. If the DRC_LOCK is equal to 1,the method continues in step 1612; otherwise, the method continues instep 1610.

[0304] In step 1612, the credits of the non-serving sector identified bythe variable count is set to the value of temporary credits.

[0305] In step 1614, the credits of the non-serving sector identified bythe variable count are set to 0.

[0306] In step 1610, the DRC_LOCK of the non-serving sector identifiedby the variable count is compared to 1. If the DRC_LOCK is equal to 1,the method continues in step 1616; otherwise, the method continues instep 1614.

[0307] In step 1616, the credits of the non-serving sector identified bythe variable count is set to the value of DRC Lock Update Interval.

[0308] In step 1618, the variable count is increased by one. The methodreturns to step 1604.

Decision Phase

[0309] In the decision phase, the AT makes a re-pointing decision inaccordance with the certified credits. In one embodiment, the ATdetermines the non-serving sectors, the certified credits of which aregreater than or equal to the soft/softer handoff delay of the sector.The AT then re-points to one of the determined sectors that has thehighest credits. If multiple sectors have equal credits, then the ATrepoints the DRC to the sector with the best forward link.

[0310] The Decision phase in accordance with one embodiment isillustrated in FIG. 17.

[0311] The method starts in step 1702, in which a variable count is setto zero. The method continues in step 1704.

[0312] In step 1704, the variable count is tested against an active setsize. If the variable count is greater than the active set size, themethod continues in step 1716, otherwise, the method continues in step1706.

[0313] In step 1706, the temporary credits of the sector identified bythe variable count are compared to the soft (or softer) handoff delayfor the non-serving sector (NS_S_Th) identified by the variable count.If the credits are less than the soft (or softer) handoff delay for thenon-serving sector (NS_S_Th) identified by the variable count, themethod continues in step 1710; otherwise, the method continues in step1712.

[0314] In step 1710, the re-pointing flag is set to zero. The methodcontinues in step 1714.

[0315] In step 1712, the re-pointing flag is set to one. The methodcontinues in step 1714.

[0316] In step 1714, the variable count is incremented. The methodreturns to step 1704.

[0317] In step 1716, the sectors with a re-pointing flag set to 1 aresorted in accordance to the sectors' accumulated credits. The methodcontinues in step 1718.

[0318] In step 1718, a test is made whether two or more sectors haveequal value of the accumulated credits. If the test is positive, themethod continues in step 1720; otherwise the method continues in step1722.

[0319] In step 1720, the AT re-points to the sector with the greatestvalue of a forward link SINR. The method continues in step 1724.

[0320] In step 1722, the AT re-points to the sector with the greatestvalue of the accumulated credit. The method continues in step 1724.

[0321] In step 1724, the accumulated credits of all sectors areinitialized to zero. The method returns to the Demodulation phase.

Re-pointing Using Only Forward Link

[0322] In all previously described embodiments, the re-pointing decisionwas made by the AT 104 in accordance with a condition of both a forwardand a reverse links. As discussed, the AT 104 can also make there-pointing decision in accordance with a condition of a forward link ora condition on a reverse link. In accordance with another embodiment,the AT 104 makes the re-pointing decision in accordance with a conditionof a forward link only. Because no feedback from a sector to an AT isprovided, all processing is carried out at the AT.

Access Terminal Processing

[0323] The processing method at the AT in accordance with the embodimentcomprises the phases of (i) Initialization, (ii) Credit Accumulation,and (iii) Decision, as described in reference to paragraph 1.2, andassociated FIGs, modified as follows.

Initialization

[0324] During the initialization stage, the AT 104 selects a sector withthe best forward link quality metric, i.e., the highest SINR, as theserving sector. The AT 104 sets the DRC for the selected sector“in-lock” and initializes credits for all non-serving sectors to zero.

[0325] In one embodiment, only one type of credits—switching credits—isdefined.

[0326] Consequently, in FIG. 4 and the accompanying text only theswitching credits are initialized to zero in step 412.

Credit Accumulation

[0327] The switching credits are used to qualify a non-serving sectorfor re-pointing.

[0328] The switching credits (CS_NS) are incremented if a forward linkSINR of the non-serving sector (FL_NS) is greater than a forward linkSINR of the current serving sector (FL_SS) modified by a pre-determinedvalue (FL_SINR_Th). The CS_NS are decremented if the above condition isnot satisfied.

[0329] The pre-determined value FL_SINR_Th is selected so thatre-pointing to another sector results in an increase in forward linkSINR and, consequently, in an increase in an average requested datarate.

[0330] In one embodiment, the minimum value for the credits is zero, andthe maximum for the credits is equal to a soft handoff delay or a softerhandoff delay. The delay used is determined based on whether or not thenon-serving sector is in the same cell as the serving sector. If thenon-serving sector is in the same cell as the serving sector then thesofter handoff delay is used, and if the non-serving sector is in a celldifferent from the one that the serving sector is part of, then the softhandoff delay is used.

[0331] The credits, initialized to zero in the Initialization phase, areaccumulated during the Credit Accumulation phase. Consequently,referring to FIG. 5, and the accompanying text, steps 510, 511, and 514are deleted. Furthermore, step 508 is modified as follows:

[0332] In step 508, a forward link SINR of a sector designated by thevariable count is compared against forward link SINR of the currentserving sector modified by the FL_SINR_Th. If the forward link SINR ofthe sector designated by the variable count is greater than the forwardlink SINR of the current serving sector modified by the FL_SINR_Th, themethod continues in step 516; otherwise, the method continues in step512.

Decision

[0333] Because no feedback information about the reverse link ispresented to the AT, the sector selection is carried out in accordancewith the switching credits.

[0334] To carry out the decision, the AT first ascertains if any of thenon-serving sectors has switching credits greater than a thresholddetermined by the soft/softer delay (NS_S_Th) for the non-servingsector. (Thus, threshold is the same for both the switching andmonitoring credits.) If at least one of the non-serving sectors hasswitching credits greater than the threshold, the AT re-points its DRCto the sector with the highest switching credits. If two or morenon-serving sectors have equal switching credits, the sector with thehighest current quality forward link is selected.

[0335] If none of the non-serving sectors has sufficient switchingcredits to mandate re-pointing, the AT continues pointing its DRC to thecurrent serving Access Point.

[0336] The decision phase in accordance with one embodiment isillustrated in reference to FIGS. 7 and 8 and the accompanying text. Inreference with FIG. 7, steps 714 through 722 are deleted. Steps 710 and712 are modified as follows:

[0337] In step 710, a value of the variable Cand_S identified by thevariable count is set to 0. The method continues in step 724.

[0338] In step 712, a value of the variable Cand_S identified by thevariable count is set to 1. The method continues in step 724.

[0339] Referring to FIG. 8, the sector selection from FIG. 7 continues.In reference with FIG. 8, steps 822 through 838, and 842 through 846 aredeleted. Steps 814, 818, and 820 are modified as follows:

[0340] In step 814, the value of the variable CS_NS_count isascertained. If the value of the variable CS_NS_count is equal to 1, themethod continues in step 816. If the value of the variable CS_NS_countis greater that 1, the method continues in step 818. Otherwise, themethod continues in step 840.

[0341] In step 818, the AT re-points the DRC to the candidate sectoridentified by the variable count that has the highest quality forwardlink. The method continues in step 820.

[0342] In step 820, the variable CS_NS is set to zero. The methodreturns to the credit accumulation phase.

[0343] Those of ordinary skill in the art will recognize that althoughthe various embodiments were described in terms of flowcharts andmethods, such was done for pedagogical purposes only. The methods can beperformed by an apparatus, which in one embodiment comprises a processorinterfaced with a transmitter and a receiver or other appropriate blocksat the AT and/or AP.

[0344] Those of skill in the art would understand that information andsignals may be represented using any of a variety of differenttechnologies and techniques. For example, data, instructions, commands,information, signals, bits, symbols, and chips that may be referencedthroughout the above description may be represented by voltages,currents, electromagnetic waves, magnetic fields or particles, opticalfields or particles, or any combination thereof.

[0345] Those of skill would further appreciate that the variousillustrative logical blocks, modules, circuits, and algorithm stepsdescribed in connection with the embodiments disclosed herein may beimplemented as electronic hardware, computer software, or combinationsof both. To clearly illustrate this interchangeability of hardware andsoftware, various illustrative components, blocks, modules, circuits,and steps have been described above generally in terms of theirfunctionality. Whether such functionality is implemented as hardware orsoftware depends upon the particular application and design constraintsimposed on the overall system. Skilled artisans may implement thedescribed functionality in varying ways for each particular application,but such implementation decisions should not be interpreted as causing adeparture from the scope of the present invention.

[0346] The various illustrative logical blocks, modules, and circuitsdescribed in connection with the embodiments disclosed herein may beimplemented or performed with a general purpose processor, a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a field programmable gate array (FPGA) or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

[0347] The steps of a method or algorithm described in connection withthe embodiments disclosed herein may be embodied directly in hardware,in a software module executed by a processor, or in a combination of thetwo. A software module may reside in RAM memory, flash memory, ROMmemory, EPROM memory, EEPROM memory, registers, hard disk, a removabledisk, a CD-ROM, or any other form of storage medium known in the art. Anexemplary storage medium is coupled to the processor such the processorcan read information from, and write information to, the storage medium.In the alternative, the storage medium may be integral to the processor.The processor and the storage medium may reside in an ASIC. The ASIC mayreside in a user terminal. In the alternative, the processor and thestorage medium may reside as discrete components in a user terminal.

[0348] The previous description of the disclosed embodiments is providedto enable any person skilled in the art to make or use the presentinvention. Various modifications to these embodiments will be readilyapparent to those skilled in the art, and the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention. Thus, the present invention is notintended to be limited to the embodiments shown herein but is to beaccorded the widest scope consistent with the principles and novelfeatures disclosed herein.

[0349] A portion of the disclosure of this patent document containsmaterial, which is subject to copyright protection. The copyright ownerhas no objection to the facsimile reproduction by anyone of the patentdocument or the patent disclosure, as it appears in the Patent andTrademark Office patent file or records, but otherwise reserves allcopyright rights whatsoever.

What is claimed is:
 1. An apparatus for directing communication betweena remote station and a plurality of sectors in a data communicationsystem, the remote station including a list of eligible sectors, theapparatus comprising: means for determining at the remote station aquality metric of a forward link for each sector in the remote station'slist; means for determining a quality metric of a reverse link to eachsector in the remote station's list, said means for determining thequality metric of the reverse link to each sector in the remotestation's list comprising means for processing at the remote station theforward link from each sector in the remote station's list, said meansfor processing at the remote station the forward link from each sectorin the remote station's list comprising: means for ascertaining a firstsignal value at a position in a first channel of the forward link for atleast one sector in the remote station's list; means for determining thequality metric in accordance with said ascertained first signal valuefor the at least one sector in the remote station's list; means forascertaining a second signal value at a position in a second channel ofthe forward link for remaining sectors in the remote station's list; andmeans for determining a second quality metric in accordance with saidascertained second signal value for the remaining sectors in the remotestation's list; and means for directing communication between the remotestation and one sector from the sectors in the remote station's list inaccordance with said determined quality metric of a forward link andsaid determined quality metric of a reverse link, said means fordirecting communication between the remote station and one sector fromthe sectors in the remote station's list comprising: means for assigningcredits to each sector in the remote station's list except the sectorcurrently serving the remote station in accordance with said determinedquality metric of a forward link, said determined quality metric of thereverse link, and said determined second quality metric of the reverselink; means for directing communication between the remote station andone sector from the sectors in the remote station's list in accordancewith said assigned credits; means for decreasing credits of a sector ifsaid determined second quality metric of the reverse link for the sectorand said determined second quality metric of the reverse link for asector currently serving the remote station are greater than a secondthreshold; and means for decreasing a first type of credits of a sectorif said determined quality metric of the reverse link for the sector isinsufficient, or if said quality metric of a forward link of the sectoris less than the quality metric of the forward link of the sectorcurrently serving the remote station, and said first quality metric ofthe reverse link for a sector was not determined.
 2. The apparatus ofclaim 1, wherein said means for decreasing a first type of creditscomprises means for decreasing switching credits of the sector.
 3. Theapparatus claim 1, further comprising: means for increasing the firsttype of credits of a sector if: the sector's quality metric of a forwardlink is greater than the quality metric of the forward link of thesector currently serving the remote station; and the sector's determinedsecond quality metric of the reverse link is less than the secondthreshold; or if: the sector's quality metric of a forward link isgreater than the quality metric of the forward link of the sectorcurrently serving the remote station; and the sector's determinedquality metric of the reverse link is sufficient; and means forincreasing a second type of credits of a sector if: the sector's qualitymetric of a forward link is greater than the quality metric of theforward link of the sector currently serving the remote station; saiddetermined second quality metric of the reverse link of the sector'squality metric of a reverse link is greater than the second threshold;and said determined second quality metric of the reverse link of thesector currently serving the remote station is less than the secondthreshold.
 4. The apparatus of claim 1, wherein said means forincreasing a second type of credits comprises means for increasingmonitoring credits of the sector.